Control apparatus



July 2 6, 193 8 R..HII\RRIS /DN ET AL CONTROL APPARATUS Filed July 18, 1935 1o Sheets-Sheet 1 v INVENTOR- THOMAS R HARRISON FREFQERICK w. SIDE A TTORNEY I July 26, 1938. 1'. R. HARRISON ET 'AL 2,125,109

CONTROL APPARATUS 7 Filed July 18, 1935 10 Sheets-Sheet 2' 7 D? D v l EC G E l FH I FIG. 3. w H fi-j 1 h INVENTOR.

. 7 no THOMASR. HARRISON FREDERICK w. SIDE A ATTORNEY July 26-, was.

'r. R. HARRISON ET AL I 2,125,109

CONTROL APBARATUS Filed July 18 49:55

1o Sheets-Sheet s INVENTOR. THOMAS R. HARRISON BY FREDERICK W. SIDE ATTORNEY July 26, 1938. 'r. R., HARRISON ET AL 2,125,109

CONTROL APPARATUS Filed July 18, 135- 1o Sheets-Sheet 4 July 26, 1938; T. R. HARRISON ET AL CONTROL APPARATUS Filed July 18, 1935 10 Sheets Sheet 5 I 'INVEN TOR.

THOMAS R. HARRISON FREDERICK w. sum-z (7L5T W ATTORNEY July 26,1938. 1R. HARRISON ET AL 2,125,109

CONTROL APPARATUS Filed July 18, 1935 10 Sheets-Sheet 6 INVENTOR;

THOMAS R. HARRISON FREDERICK w. SIDE July 26, 1938. T. R. HARIRISGNI ET AL CONTROL APPARATUS Filed July 18-, 19:55 10 Sheets-Sheet I6 IIII INVENTOR. THOMAS R. HARRISON FREDERICK W. SIDE ATTORNEY July 26, 1938. T. R HARmsoN ET AL 2,125,109

CONTROL APPARATUS Filed July 18, 1955 lo Sh96t$She et 8 ENTOR. THOMAS R. HARRISON FREDERICK w. SIDE BY 5 l ATT ORNEY g Jy 6, 1938., I T. R HARRISON ET A1. 1

CONTROLQAPBARATUS Filed July 18, 1935 10 Sheets-Sheet 9 FIG. B6.

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INVENTOR. THOMAS R. HARRISON FREDERICK W. SIDE BY I a ATTORNEY T. R. HARRISON ET AL CONTROL APPARATUS Filed July 18,: 1935 July 26, 1938.

10 Sheets-Sheet 10 B m. F

lllmm INVENTOR.

THOMAS R. HARRISON FREDERICK W. SIDE J g I /M5Q ATTORNEY Y Patented July 26, 1938 1 UNITED STATES PATENT OFFICE 2,125,109 coN'rnoL APPARATUS.

Application July 18, 1935, Serial lilo. 32,028

69 Claims.

The general object of the present invention is to provide improved control apparatus of the type comprising an element deflecting in accordance with changes in the value of a controlling quantity or condition, meansthrough which the deflection of said element from a predetermined, or normal value, position of the element varies an air or other control force, and means through which the variation in the control force thus produced, modifies the action of said element on the first mentioned means so as to effect suitable corrective variations in the control force on a departure of the latter from its predetermined or normal value, without creating an ohi jectionable tendency to unstable control, or hunting.

More specific objects of the invention are to provide improvements in air actuated controllers of the type devised by us and forming the subject matter of our prior application No. 693,388, filed October 12, 1933. The controller disclosed in said prior application comprises an air space, valve means regulating a control pressure maintained insaid space, a device for effecting an adjustment of said valve means on a change in a control condition to which said device is responsive, to thereby vary the pressure in said space, and a mechanism which is responsive to changes in said pressure and is actuated on an initial change therein produced by the adjustment of said valve means by said device to give said valve means a second, or follow up, adjustment tending to a reverse change in said pressure, and thereafter a third, or compensating adjustment in the direction to eliminate said second adjustment.

For the maintenance of the desired pressure in said space, the latter is provided with an inlet port through which said space receives air under suitable pressure and an outlet port through which air may escape from said space, and the said valve means may'comprise a valve seat member in-which one of said is formed and a valve member moved relative to the valve seat member, on the adjustment of said valve means, to thereby variably throttle the last mentioned port;

Our improved controller, disclosed and claimed herein, comprises mechanism through which the effect of a pressure change in the said air space resulting from an adjustment of the valve means by the device responsive to the control condition, controls the timing and in some cases the magnitudes .of the resultant second and third adjustments relative to each other, and/or in respect to the relation of each to the valve means adjustment eflected by said device on a change in said condition.

Air actuated controllers embodying the fea tures of our present invention and of our said perature,-a pressure or a velocity, which may or may not vary, or tend to vary, as a result 'of the control eflect produced. In general, however, the relative magnitudes and timing of the second and third adjustments resulting from the change in the control pressure effected by, and following a change in the control pressure produced by an initial adjustment of the valve means by the device responsive to the control quantity, will depend on the character of the control system and the operating conditions. When, as in the control of the heat supplied to a furnace in response to a furnace temperature or heating effect, the response of the control quantity to a corrective adjustment in the pressure fuel supply, is delayed as a result of the so-called furnace lag, or in any control system in which the effect of a change in the control quantity is delayed by inertia, so to speak,,of the apparatus controlled, variation in the relative magnitudes and timing of the dlflerent adjustments of a cycle of adjustments for which we make provisions, must be made to insure optimum control results, so as to make proper allowance for furnace lag or analogous inertia characteristic of the controlled apparatus.

For use in furnace control, and for many other purposes, it is ordinarily desirable to provide for adjustment of the control apparatus so that it tends to maintain a predetermined normal value of the controlling quantity or condition which value may vary from time to time, and our present invention comprises improved means for the adjustment oi the normal value of a control quantity which it tends to maintain.

The various features of novelty which characterize our invention are pointed out with particularity in the claims annexed to and forming' apart of this specification. For a better understanding of the invention, however, and the advantages possessed by it, reference should be had to the accompanying drawings and descriptive matter in which we have illustrated and tijescribed a preferred embodiment of the inven- Of the drawings:

Fig. 1 is a front elevation of a control instrument with parts broken away and in section;

Fig. 2 is a partial section on the line 2- -2 of Fig. 1;

Fig. 3 is a diagrammatic representation of a control system including the instrument shown in Figs. 1 and 2;

Fig. 4 is a rear elevation partly in section, of parts shown on smaller scale in Fig. 3;

Fig. 5 is a front elevation, on a larger scale than Fig. 1, of a portion of the instrument shown in Fig. 1;

Fig. 6 is a side elevation, of parts shown in Fig. 5;

Fig. '7 is a side elevation of a second form of control instrument;

' Fig. 8 is an elevation partly in section and taken at rightangles to Fig. 7; I

Fig. 9 is a diagrammatic representation 'of parts shown of Figs. '7 and 8 and relatively displaced to better show their construction and ar- .ran gement;

Fig; 10 is a perspective view of a portion of a third form of control instrument;

Fig. 11 is an elevation of a portion of an in- Fig. 16 is a side elevation of a portion of a sixth form of control instrument;

' Fig. 17 is a partial elevation taken at right angles to Fig. 16;

Fig. '18 is a. side elevation of a portion of still another form of control instrument;

Fig. 19 is a partial elevation taken at right angles to Fig. 18; and

Fig. 19A is a modification vof a detail of our invention. a

The particular form of control system diagrammatically shown by way of example in Fig. 3, is adapted to adjust a fuel supply valve or other controller a, to thereby regulate the supply of heat to a furnace A as required to maintain an approximately constant furnace temperature which is measured by an expansion fluid thermometerof which B is the temperature responsive bulb or chamber. The fluid pressure in chamber B, which increases and decreases as the furnace temperature rises and falls, is transmitted by a conduit b to a pressure responsive element C, shown as a Bourdon tube of helical form having its stationary end connected to the conduit 17, and having its movable end secured to an arm C, which is pivoted to turn about an axis 0, clockwise or counter-clockwise, as the pressure in the tube rises or falls.

Throughsuitable connections, the oscillations of the arm C give motion to the valve of, which as shown, forms a part of a control pressure regulator or air controller unit or device D, and regulates the escape of air from, and thereby regulates the control air pressure in the regulator chamber D. The latterv receives air through a pipe E, a coupling EA and pipe EB from air supply means, which as shown, comprises a chamber F receiving air under pressure through a supply pipe G, and comprises means for maintaining. a substantially constant pressure in the chamber, somewhat smaller than the pressure in the pipe G, notwithstanding fluctuations in the last mentioned pressure. The flow through the pipe E into the pipe EB is restricted, as by means of restricted port E, in the cou pling EA between the'pipes, so that the pressure in the pipe EB may normally be the same as that in the chamber D, and below'that in the chamber F.

The variable air pressure maintained in the chamber D is transmitted through a pipe EC in free communication through the coupling EA, with the pipe EB, to the pressure regulator diaphragm chamber H of a fluid pressure relay device having a main pressure chamber H. The latter receives air under pressure through the passage FH from a suitable source shown as the chamber F, and means are provided for maintaining a pressure in the chamber H which varies with the pressure in the diaphragm chamber H and hence with the control pressure in the regulator chamber D'. The means shown for the purpose comprises a valve member h, actuated by the flexible diaphragm it between chambers H and H, which throttles the air inlet throughi nlet FH more or less, and the outlet of air from chamber H through a vent H, less or more, as the pressure in the chamber H, rises above or falls below the pressure in v the chamber H.

The pressure in the chamber H is transmitted by a conduit Ha to the pressure chamber a of the valve a, which is a fluid pressure valve opening and closing to increase or decrease the fuel supply to the furnace A- through a fuel supply pipe A as the control pressure in the regulator D rises and falls.

All of the above mentioned parts except the furnace A, valve 0, and bulb B may advantageously be combined in a single control instrument, and are so shown in Figs. 1 and 2.

The present invention is concerned with and consists in various mechanisms and methods by which a valve member, such as the above mentioned valve member 6, is adjusted by. and as a result of, movements of a member, such as the above mentioned arm C, in response to changes in the value of the control quantity, which in the arrangement shown in Fig. 1, is the furnace temperature to which the thermocouple B responds.

In the form of the invention illustrated in Figs. 1-6, movements of the arm 9' give movements to the valve d through a link CI, a rock ing element I, a floating lever K, a link 1K connecting parts I and K, and a bell crank lever M connected by pivot M to the lever K, and carrying a pin M engaging the valve d. The value of the control quantity which the apparatus tends to maintain may be manually adjusted as conditions make desirable, by a rocking element J connected to the lever K by a link JK. The latter in effect, forms an adjustable fulcrum for the lever K, and mechanism hereinafter described, adjusts the lever M relative-to the lever K to modify the action of the latter on the valve d, in response to variations in pressure conditions within the device D, resulting from changes in the position of the. valve d The rocking element I is mounted to oscillate about the axis of a shaft 1*, and carries a pointer I which may indicate the value of the control quantity on a suitable scale and in the instruend secured to the end head D and has its other ment CC, as shown in Fig. 1, carries a pen point or stylus at its ,free end which is adapted to make a'record on a chart disc C The latter is rotatedby the constantly rotating chart shaft CC, and is provided with scale lines. As shown,

the rocking element I includes an arm I to which the corresponding end of the link CI is connected, and a second arm I to which the correspending end of thelink IK is connected.

The rocking element J is mounted to oscillate about the axis of the shaft 1 and includes an index arm- J which indicates on the same'scale with which the pointer I cooperates, the normal 1 value of the control quantity. When the control quantity is at its normal value, the pointer I will be directly in front of, and will registeron the scale with the index J. As shown in Fig. -3, the position of the pointer I corresponds to an actual value of the control quantity greater than the normal value. The element J includes an arm J to which the corresponding end of the link JK is connected. In the valve operating means shown in Figs. 1, 3, and 5, the floating lever K is suspended fromthe arms I and J by members 1K and JK, which engage the lever K at spaced apart points and constitute substantially vertical suspension links through which the lever is suspended. tational forces are utilized in eliminating lost motion in effecting an adjustment of the lever K through either of said links by angular adjustment of the corresponding elements I or J. As previously explained, the element I is given angular adjustments in accordance with changes in the value of the control quantity acting through the parts C, C and CI. The rocking element J may be manually adjusted about the axis of the shaft I to increase or decrease the normal value indicated by the index J, and to simultaneously and correspondingly raise or lower the'fulcrum for .the lever K formed by the lower end of the link JK, by an adjusting element J having an arm J connected by a link J to the element J. As shown, theadjusting element J is in the form of a rotatable element which may be normally held stationary by frictional means, and is provided, with a kerf J for engagement by a screw driver by which the element J may be angularly adjusted to thereby angularly adjust the element J, when adjustment in the normalvalue of the control quantity is desirable.

nozzle'D through which air escapes to the, at-v mosphere from the chamber D at a rate depending on the adjustment of the valve member d.- Preferably and as shown, the nozzle member D has an external globular end surface surrounding the outer end of the nozzle passage D and the valve member d is a piece of sheet metal extending transverse to the length of, and movable toward and away from the outer end of the nozzle passage. As' shown, the valve d is pivoted to turn about a shaft d which may be mounted on the head D A spring d gives the valve d a slight bias toward its closed position, in which it engages the nozzle member D at the margin of thenozzle passage D.

A resilient bellows element D -located within, but not filling the casing of the device D, has one In consequence, graviend closed so that an increase or decrease in the pressure within the space D between the casing of the device D and the bellows D tends to contract and expand the latter. Within the bellows D and separated from the latter by an interbellows space D is a smaller bellows ele'i'nent D which has one end secured to the end head D at the margin of an opening D in the latter, through which the interior of the bellows D is in free communication with the atmosphere at all times. The inter-bellows space D communicates with'the atmosphere through a restricted passage D formed in the end head.

' Advantageously, an adjustable obturator D is provided to regulate the flowcapacity of the lows D modify the operating eifect of the lever K on the valve d, through parts which are shown best in Figs. 3-6, and comprise a link DO connecting the bellows head 13 to a lever O mounted to oscillate about the shaft (1' and pivotally connected by a pivot shaft'O to a lever L. The latter is connected by a pivot shaft M to the lever M, and has an adjustable fulcrum formed by a pivot pinL' carried. by the lever L and slidingly received in a diametral slot NT formed in an angularly adjustable disc N. Y

The linkDO which is axially disposed in the bellows D and may be rigidly secured to the end head D of the latter, is preferably connected to the lever 0 for adjustment relative to the latter', in such manner'as to vary the efiective length of the link. As shown, the lever O is a trough shaped piece of sheet metal having side portions transverse to and formed with journal apertures through which the shaft d extends, and having a bottom wall generally parallel to the end head D, and between the latter and the shaft d. The link DO extends through a bottom wall opening in the lever O, and is hooked or looped about a pivot pin 0 carried between the legs of a yoke portion 0 of a sheet metal part 0 secured to the bottom wall of the lever Oat a distance from the link DO. A threaded adjusting device 0 acts between the part 0 and the bottom wall of the lever 0 adjacent its connection to the link D0, to bend the corresponding portion of the member 0 farther away from, or to allow it to approach closer to the bottom wall of the memher 0, and thereby move the pivot pin 0 relative to the lever O in the direction of the length of the link DO. The pivot shaft 0 has its ends mounted in the sides of the trough shaped lever member 0.

As shown, the lever L comprises opposite side portions between, and respectively adjacentthe opposite side portions of'the lever O, and a cross bar connecting portion L. An uprising arm portion of the side portion of the lever L adjacent the disc N, carries the pin L which works in the slot N, so that the lever L forms in effect a bell crank lever, with the plane of its pivotal'connections O' and M at one side of the pivot pin L. The pivot shaft W passes through the side portions of the lever L.

Counterclockwise movement of the lever M about its pivot M, as seen in Fig. 4, gives an opening movement to the'flapper valve d through the action on the latter of the pin M? carried by the lever M. The pin M- is advantageously connected to the lever M for movement toward and away from the pivot Mto thereby vary the extent of valve movement produced by a given angular movement of the lever M. For the purposes of this adjustment, the pin M is mounted in, and extends through a link M which is formed with a longitudinal slot for the passage of a screw M for clamping the link M to the lever M with the pin M at different distances from the clamping screw M 'As the eflective length of the link M is thus varied, thepin M moves toward or away from the pivot M in a slot M in the lever M extending radially from the pivot M To adapt the apparatus for use under conditions in which a clockwise movement of the lever M, as seen in Fig. 4, should give an opening adjustment to the valve, the lever M is formed with a second slot M generally in alignment with the slot M, but at the opposite side of the pivot M and adapted to form a slideway for the pin M when the link M is suitably positioned for that purpose.

The member N is supported by a bracket D mounted on the end head D and extending transversely to the latter and formed with an aperture D coaxial with the disc N. The latter is adjustably held against the bracket D by two angularly displaced clip'parts N shown as bolts threaded into the bracket and having cylindrical body portions engaged by the edge of the disc, and head portions which overlap the outer portion of the disc, and by a third clip part N3 comprising a bolt or pin attached at one end to the bracket D and a sliding collar N pressed by a spring N toward the bracket. The head N is formed with a conical surface which bears against the edge of the disc N. The clip parts N and N thus collectively provide a bearing for the disc N, in which the latter may be angularly adjusted by means of an extension arm N. The latter as shown, is provided with an index line cooperating with a scale D on the bracket D to indicate the angular adjustment or direction of inclination of the slot N, in which the pin L' of lever L is received. The spring pressed part N insures the frictional holding of the disc N in any angular position into which it may be adjusted.

Each of the bellows elements D and D has longitudinal resilience and, consequently, a definite length when the pressures acting on its inner and outer walls are the same. When the external pressure on either bellows is less than, or exceeds the pressure within the bellows, the bellows will elongate or contract as require to make the diiferential of the effects of thosepressures on the bellows equal to the opposing resilient bellows force resulting from the elongation or contt'fiaction of the bellows, that force, of itself, always tending to return the bellows to its normal or unstressed length.

0nv an increase in the pressure within the Bourdon tube C and consequent movement of the link IK upward as seen in Fig. 3, the lever M acts on the valve 11 to move the latter away from the nozzle D and thereby reduce the pressure in chamber D. ber D elongates the bellows D and thereby enlarges the interbellows space D and reduces the pressure in the latter, owing to the relatively slow inflow of air permitted by the restricted passage D The reduction of the pressure in the space D elongatesthe bellows D and thereby moves the link D0 to the right as seen in Fig. 3. The movement thus given the lever 0, moves the parts L M, and K toward the right as seen in Fig. 3, and thereby permits of a return move-- ment'of the. valve it toward the nozzle D par- The pgessure reduction in chamcalled a foudwmp adjustment tially neutralizing the efiect of its initial movement away from the nozzle.

The extent of such return movement of the valve d produced by a given movement of the link DO, depends, with the arrangement shown in Figs. 1-6, upon the relation of the movement of the pivotal connection M to the movement of the pivotal connection 0', and that relation is dependent upon the inclination of the slot N' in the member N. With the slot N inclined generally as shown in Fig. 3, a counter-clockwise turning movement of the lever 0 about the shaft d will produce a clockwise or counter-clockwise movement of the lever L about the pivotal connection O accordingly, as the direction of the length of the slot N diverges counter-clockwise or clockwise, respectively, from the direction of the plane including the axes of the shaft 0' and. pin L. With the adjustment of the disc N such that the counter-clockwise movement of the lever causes the lever L to turn clockwise about the shaft 0', the angular movement of the pivot M about the shaft d will be less than the angular movement about the latter of the lever 0'.

The enlargement of the interbellows space or chamber D reduces the pressure therein and thereby creates an inflow of air into D through the passage D which tends to slowly restore the pressure in the chamber D to its normal equality with the pressure of the atmosphere. As the pressure in the chamber D builds up, the bellows D shortens and thereby again moves the valve d away from the nozzle D and back toward the position into which it was moved on the original change in position of the link IK, provided the latter has not been moved in the direction of its length in the meantime as a result of a change in the Bourdon tube pressure. The converse of the actions just described occur on a decrease in the pressure in the Bourdon tube C, and a corresponding adjustment of the link IK downward as seen in Fig. 3.

In the normal and intended use of the apparatus shown in Figs. 1-6, the proportions and adjustments of the parts are such that upon an increase or decrease in furnace load of usual magnitude requiring some increase or decrease in the rate of fuel supply to maintain the desired furnace temperature, the initial resultant decrease or increase in the furnace temperature will tend to produce a movement to its limit, of the valve controlling the rate of fuel supply, in the direction to return the control temperature to its normal value, which will therefore be of such magnitude that the new rate of fuel supply will be greater or less, respectively, than that required to maintain the normal control temperature with the new furnace load. Such a control operation of itself. is essentially unstable, and

must result in hunting. The control action described is modified, and the hunting tendencyeliminated or minimized by the initial movement of the link D0, which effects what is commonly The. latter can be made sufllcient to insure a control which is stable and not hunting. In such case, however,

the follow-up adjustment, if not later neutralized, will result in the maintenance of a. furnace temperature necessarily, and significantly lower with a heavy furnace load than with a lighter furnace load;

eithe'rlimit wihout reversing the control tempering a departure from that value, is a compensating adjustment which may be made to neutralize the effect of the follow-up adjustment slowly enough to substantially eliminate the effect of the follow-up adjustment on the control temperature when the load is steady, without giving rise'to an objectionable hunting tendency.

With the apparatus shown in Figs. 1-6, a heavy furnace load requires the combustion of more fuel, and hence a higher pressure in the valve chamber a, than are required by. a lighter load.

is so small as to be without significant effect on the ordinary operation of the contrwl apparatus,

and to correspond to a departure at the control temperature normal value sosmall as ordinarily to be of no significance, but I may completely eliminate the necessity for such variation of the nozzle D and valve d by providing a servo nozzle as shown in Fig. 5. The servo nozzle of Fig. 5

comprises a thin metal shell the cylindrical portion D of which is rigidly attached to end wall D and the interior of which is in free communication with space D The flexible outer wall D of the shell is adapted to expand and contract as a result of increase or decrease in pressure within the shell and accordingly within space D Aperture D in end wall D is the actual port which is variably throttled by valve d and it will be clear that with the proper proportioning of the size and thickness of the end wall, the latter may move toward or away from the nozzle to compensate for the change in relationship of the valved and nozzle W referred to above.

With the apparatus of Figs. 1-6, on any significant departure of the control temperature from its predetermined normal value, ordinarily the initial adjustment given the valve (1 by thelink IK, should be sufficient, if the valve adjustment were maintained, to vary the pressure in the chamber D to the corresponding limit, which is a pressure approximately equal to the pressure of the atmosphere when the control temperature is above normal, and is approximately equal to the pressure in the pipe E when the control temperature is below normal. Ordinarily, also, the

resultant follow-up adjustment effected as the be reversed during, or prior to an initial portion of the compensating adjustment following the initial adjustment of the valve d. If said trend is not so reversed, the pressure in D will change further in the original direction, as the compensating adjustment proceeds, and thereby prolong the compensating adjustment until the control temperature trend is reversed, or the pressure in D reaches its corresponding limit. The variation in the pressure in D will not extend to ature trend, unless furnace or load conditions require a corrective control-effect beyond the operative capacity or range of the control apparatus.

The magnitude of the follow-up adjustment and time interval in which it is effected, which will give the optimum results in any particular control system, will depend on the character. of that system and operating conditions. In particular, in furnace control it will depend largely on the so-called "time lag of the furnace, or rate of response of the furnace temperature to a corrective change in the rate of fuel supply.

In general, also, for optimum results account needs to be taken of the normal and to be expected magnitude, frequency, and duration of the changes in furnace load, or other conditions affecting the control quantity, since the particular magnitude and timing of control actions which will give the best results with one character of change in furnace load or other controlling condition, may not give the best result when those changes are of a diflerent character. Ordinarily, therefore, optimum results are those which are best adapted to cope with some assumed average or usual character of changes in a primary controlling condition.

It should be borne in mind that such a control system as that shown in Figs. 1-6, must copenot merely with individual more or less transient changes in furnace load, but with conditions which exist when one change in furnace load is followed 'by further furnace load changes in the same direction or in the opposite direction, before the control actions started by and effective to cor.- rect for the original change have been completed, so that a new follow-up adjustment is instituted before the previous follow-up adjustmentor subsequent compensating return adjustment is completed. The conditions just mentioned are not peculiar to furnace control, but exist in any control system in which the primary control condition fluctuates in a variable manner.

quantity during the time of a departure from normal of the control quantity, which may be varied by varying the inclination of the slot N in the member N to thereby vary the magnitude of the follow-up adjustment, and includes other provisions for varying the time intervals required to eliminate the follow-up adjustments. Other forms of the invention hereinafter described include other features of which no use is made in the apparatus shown in Figs. 1-6. The apparatus in the form of Figs. 1-6 was designed for producing a corrective effect whereby in a temperature installation, for example, the rate of fuel flow is adjusted to different values in proportion to the extent of temperature departure from normal, the rate of change of this rate of flow or the rate of valve adjustment, is proportional to the rate of temperature change, and the rate of fuel demand which caused the departure. Such a surplus correction may be made during the first stage of a departure from normal with advantageous results, if it is of the proper magnitude and duration to suit the particular process under control and the latter requires that the correction be removed before resulting in an over correction which would cause hunting. In the mechanism hereinafter described provisions are made for adjustably controlling the application of such greater change in the corrective agent upon a departure from normal of the controlled condition.

We preferably cause the greater initial change by delaying the follow-up movement which, in the normal operation of the mechanism of Figs. 1-6, tends to prevent large corrective action. In the arrangement shown in Figs. 7-9, the follow-up adjustment of the flapper valve, occurring as aresult of an initial change in the control quantity, may be variably delayed and varied in magnitude by means of an adjustable lost motion connection between the follow-up link DO and the flapper or control valve. Such delay effects periods during which the full effect of the tendency toward large valve adJustmehts is permitted.

7 The apparatus shown in Figs. 7-9 may be identical with that shown in Figs. 1-6, except as hereinafter noted in respect to the provisions through which the lever K and follow-up link D cooperate to control the position of the flapper valve da, generally like, and replacing the flapper valve d previously described.

In the arrangement shown in Figs. 7-9, the follow-up action link D0 is connected at its upper end to an extension 0' of a lever 0A journalled on the shaft d on which the flapper valve do is journalled.v At a distance from a shaft d, the lever 0A carries a follow-up adjustment device NA, in the form of a disc formed with a slot N, the center line of which extends circularly about the axis of a pivotal connection between the disc NA and the lever 0A. Said axis is parallel to the shaft d, and said slot N progressively increases in radial depth from one end to the other. The disc NA is pivotally connected to the lever CA- by a screw N passing through the disc NA and threaded into the lever 0A, with a fricthe disc NA, so that the latter may be frictionally held in any angular position into which it is adjusted. The disc NA and a pin L carried by the lever LA and extending through the slot N" in said disc, provide an adjustable lost motion connection between the lever 0A and the lever LA. The lever LA is pivoted on the shaft d, and is yieldingly held in any angular position intowhich it is adjusted, by means of its extension L having a surface extending circularly about the axis of the shaft d, and engaged by a friction spring L secured to the head D of the unit D. The lever LA supports a pivot shaft L which is adjacent the pin L and between the latter and the shaft d,

ing generally to the lever M of the construction first described, the lever K being connected to one arm of the lever MA, while the other arm of the lever MA carries a pin M through which the pin M' engages asurface d3 carried by an arm or extension of the valve do, and inclined to the plane which passesthrough the axis of the shaft d and is tangential to the flapper valve seat at the outer end of the nozzle member D The.

With the parts of the arrangement shown in Figs. 7-9 already described, on any change in the value of the quantity measured, the link IK acts through the levers K and MA. to producev a corresponding adjustment of the flapper valve da, generally, as a similar quantity change produces analogous flapper valve movements, through the lever K, and lever M of the arrangement of Figs. 1-6. In the arrangement of Figs. 7-9, also, any movement of the follow up link DO produces a corresponding movement of the lever 0A about the shaft d.

The movement of the lever 0A produced by the link D0 is without effect on the flapper valve position, however, unless and until its extent is sumcient to bring one edge or the other of the slot N into engagement with the pin L Thereafter if the movement of the lever 0A continues, the lever LA is similarly moved, with a resultant change in the position of the pivot shaft 1? on which the lever MA is journalled, and such adjustment of the lever MA has the same effect on the position and operation of theflapper valve do, as the adjustment of the lever M produced by the lever O has on the valve d of Figs. 1-6. The extent of the lost motion between the levers LA and 0A permitted depends upon the radial extent of the portion of the slot N in which the pin L is located, and may be varied by angular adjustment of the disc NA. The efiect of said lost motion is to delay, and to minimize the extent of, the eifect on the position of the flapper valve do, produced by a given movement of the link OD.

Advantageously, and as shown, the arrangement of Figs. 7-9, includes bias means tending to hold the lever 0A in a predetermined normal angular position, and to hold the lever LA in a corresponding normal angular position, in which the axis of the pin L intersects the center line of the tapered slot N. The bias means shown, comprises a lever P turning above a pivot shaft P which is mounted on the head D and parallel to the shaft d'. A spring P tends to move the lever P into a normal position of the latter,

in which it engages portions 0' and 0 of the lever CA at opposite sides of the shaft d', and engages portions L and L of the lever LA at the opposite sides of the shaft d, and thus holds each of the levers 0A and LA in a corresponding normal position. As shown, the lever P is formed at its edge adJacent the head Dwith projections P P and P In the normal positions of the levers 0A, LA and P, the projection P engages the portion 0" of the lever 0A, and the projection P engages the portion L of the lever LA, and the projection P engages both the portion 0 of the lever 0A, and the portion L of the lever LA.

As will be apparent, turning movement of the lever 0A under the action'of the link D0 in either direction, will turn the lever P clockwise as seen in Fig. 9, against the action of the spring P To avoid gravitational effects, the lever LA is advantageously provided with an arm L' carrying a counterweight L which may be adjusted as required to balance the gravitational forces acting on lever LA, including any thrust on the lever by the lever MA. The tension of the spring As shown, the abutment P may be adjusted through a supporting nut P" threaded on a screw P secured to the head D", and generally parallel to the spring P The return of the levers A and LA to their normal positions by the lever P at the end of any one adjusting operation or cycle, insures the desired extent of lost motion between.the levers LA and CA on the initial movement of the latter in either direction from its normal position at the beginning of a following control op- The action of the return to normal lever P with its loading spring P on the lever OA, also modiflesthe extent and time required for each follow up adjustment and for each compensating adjustment. prevents the bellows D from contracting or elongating, as a result of a difference between the pressures acting on its inner and outer sides, ex-

cept when that pressure differential is large enough to overbalance the effect on the bellows bellows space D rises above atmospheric pressure,'the, bellows D will not begin to contract until the rise is sufficient to overbalance the action on the bellows of the spring P Conversely, the pressure in D must fall below the pressure of the atmosphere by a predetermined amount, before the action of the spring P will permit the bellows D to elongate.

The return to normal lever P with its spring P therefore retards the initiation of each follow up adjustment and hastens the completion of the subsequent compensating adjustment, and thus tends to shorten the period in which each such adjustment is'effected. Moreover, the lever P with its loading spring reduces the extent of the movement given the free end of the bellows D by any given change in the pressure in D, and thereby not only reduces the magnitude of the follow up adjustment, but also the magnitude of the subsequent compensating adjustment.

In thearrangementshown in Figs. 7, 8, and 9 the levers P and 0A coact as levers of the second and first classes, respectively. On an elongation of the bellows D, the lever P applies power to the projection 0 carried by one arm of the lever 0A. When the bellows D contracts, the lever P acts on the projection carried by the second arm of the lever 0A. 11' the length of the two lever arms of lever 0A are in the same proportion as the distances from the fulcrum P' to the portions of the lever P, respectively engaging the parts 0 and 'O' of the lever 0A, the modifying effect of the lever P on the follow up and compensating adjustments will be the same, when the adjustments result from a conproportional, not to the full movement given the link DO but only to the portionof that move- The spring P on the flapper valve supporting shaft d.

ment occurring after the lost motion has been taken up so that one or the other of the curved edges of the slot N is brought into engagement with the pin I. carried by the lever LA. The lost motion connection between the levers LA and 0A also serves to permit any reverse change in the control quantity, resulting either from a change in furnace load or other primary control condition, or as a result of the corrective adjustment of the controlled quantity following the initial departure of the control quantity from its justment.

The arrangement shown in Figs. 10 and 11 includes provisions, different from, and somewhat simpler than those shown in Figs. 7-9, for a lost motion connection between the follow-up link DO and the flapper valve, giving the same general effects of the lost motion connection of Figs. 7-9. The arrangement of Figs. 10 and 11 include nothing analogous in effect, or operative result, to the lever P of Figs. 7-9, however. In the mechanism of Figs. 10 and 11 are embodied, however, further provisions governing the removal of the initial effect produced by the lost motion connection. In the device of Figs. 7-9, the initial eil'ect produced as a result of the lost motion connection will remain applied until the trend of the controlled condition reverses, because, as will be .clear, the direction of the subsequent compensattion from its'original rotation, as a result of the return of the controlled condition toward normal. It is sometimes desirable to remove the initial correction as soon as the trend of the condition away from normal is halted or has been checked. The apparatus of Figs. 10 and 11 is adapted to remove the initial effect as soon as the rate of departure of the condition from the control point falls below the rate of compensation or, for example, what wouldbe the equivalent in Figs. 7-9, of the removal of the large initial effect when the rate of movement of member MA by lever K in one direction is less than the movement of member MA, in the same direction, by link DO as the pressure equalizes across restriction D The latter action is desirable because such a condition indicates the trend of the departure has been checked, and the large initial eflect if not removed would result in reversing the trend, and possibly cause an overswing in the opposite direction.

In Figs. 10 and 11, the follow-up link D0 is connected and gives motion to a lever OB pivoted The free end of the lever OB supports a pivot shaft 0 parallel to the shaft d and on which is journalled a leverLB carrying a pivot L on which a lever MB is journalled. The latter is connected to the lever-K and may be identical with the previously described lever MA but as shown, differs from the latter in that its flapper valve operating pin M is adjustably connected to the lever MB as the pin M is connected to the lever M in the construction shown in Figs. 1-6. At the opposite side of the pivot shaft 0 from the pivot L the lever LB has mounted on' it an angularly adjustable slotted disc NB, which may be exactly like the discNA mounted on the lever 0A of Figs. 7-9. a

The relative angular movement of the levers a link 0L, and intermediate its ends, the lever 0L carries a pin 0L which works in the slot N of the disc NB of Figs. 10 and 11, as the pin L works in the slot of the disc NA. The abutment member OL -to which lever OL is connected by link 0L is adjustably clamped to an extension D from the head D by a clamping screw 0L passing through an arc shaped slot D in the extension D". The abutment 0L is thus adjustable in the direction of the length of the slot D which may be, and as shown, extends circularly about an axis approximately coincident with the axis of the pin OL when the latter is in the center of slot N.

The lever LB carries another pin L engaged by a flat spring L The latter is pivoted on the flapper valve shaft 12', but is yieldingly held against movement about said shaft by its frictional engagement with a bracket (1 in which the shaft d is journalled. The spring L does not significantly oppose turning movement of the lever LB about the axis of pin L but does oppose movement of that pin angularly about shaft (1'. The pin L is displaced from pivot L so that movements of lever LB, independently of lever 0B which are pivotal movements about pin L result in rotation of pin L about the axis of pin L to thereby eflect movement of the flapper valve when relative movements of the pivot shaft O and 0 are unrestrained. Such free relative movements of shaft 0 and pin L may occur only scribed, as that mechanism is seen in Fig.11, on

a clockwise adjustment of the lever MB produced by the lever K and giving an opening adjustment'to the flapper valve db, the resultant downward follow-up movement of the link DO turns the lever OB counterclockwise about the shaft (1' and thereby lowers the pivot shaft 0 Such movement of the pivot shaft 0 causes the lever LB to turn clockwise about the axis of pin L which turns pivot L in the clockwise direction lifting flapper db further from the nozzle thereby amplifying the original flapper movement. This movement will continue until the lowering of the disc NB brings the upper wall of the disc slot N into engagement with the pin 0L Therefore a continuation of the downward movement of the shaft 0 will cause a counterclockwise movement of the pivot L about the pin 01. as a result of the link connection between the lever 0L and the stationary abutment 0L Such movement of the pivot L lowers the lever MB and gives a closing movement to the flapper valve db which partially neutralizes the opening movement of that valve produced by the previously mentioned initial action of the lever K. If the movement oi lever K is then terminated, as it will be when the trend of the condition has stopped, the upward movement of link DO as a phere, will move link OB clockwise about :1 thereby turning lever LB about L to close the valve db. This movement will continue until terminated by engagement of pin 0L with the bottom of slot N when the initial eifect will have been removed and thereafter the normal compensating action of bellows D will result in turning lever LB about the point of engagement of pin 0L and the bottom of slot N in the clockwise direction to gradually open the valve. Similarly, when the rate of movement of lever K slows down to the extent that the opening movement of the flapper resulting from the clockwise rotation of lever MB about its pivot L is less than the closing movement of the flapper resulting from the rising of the link DO and coincident counterclockwise movement of LB, the flapper will be given a closing movement tending to remove the initial effect, and when the pin OL is thereby contacted by the bottom of slot N the subsequent compensating movement of link D0 will gradually open the valve.

Various actions may occur in the mechanism of Figs. 10 and 11 depending on the rate of movement of lever K and link DO. If their eilective movements are equal and opposite for such time as is necessary to bring pin OL into contact with the opposite side of slot N the initial effect will not be removed and the effect of further movement of link D0 will be added to the effect of the further movement of lever K to counteract the condition change. On a reversal of the trend lever K would be rotated in the reverse direction promptly removing the initial effect as will be clear from the foregoing. With this mechanism we therefore obtain a control action which includes a large initial effect, calculated to arrest and reverse the trend of the condition, which is removed in response to the subsequent trend of the condition and is combined with the followup and compensating control actions of the de vice of Figs. 1-6.

With the mechanism of Figs. 10 and 11, moreover, the magnitude of the follow-up adjustment eventually produced may be varied in a manner analogous to that in which it is' varied with the apparatus shown in Figs. l-6, by adjustment of the abutment member 0L along the slot D". This follows from the fact that the link OL connecting the abutment 0L to the lever 0L causes more or less turning movement of the lever LB about the pivot shaft 0 when the pin 0L is in engagement with either curved wall of the slot N in the disc NB, accordingly as the abutment 0L is anchored in one position or another along the length of the slot D In general, in any particular control installation, and so long as the general conditions of operation are unchanged, r

it will be found that optimum control results are obtained with some particular position of the abutment member 0L along the slot D With the apparatus of Figs. 10-11, as with that of Figs. 7-9, the initiation of each compensating adjustment is delayed, following the completion of the preceding follow-up adjustment, during the time required for a relative movement of the pin and slotted lost motion disc, corresponding to the width of the slot in the latter. In this respect, the operation of the apparatus of Figs. 7-11 is analogous to that shown in Fig. 12, in which a difierent form of lost motion connection is employed. In respect to the variation in relative magnitudes of the follow-up and compensating adjustments under certain different conditions,

the operation of the apparatus of Fig. 12 is analogous to that of the apparatus of Figs. 10 and 11'.

Fig. 12 illustrates a third arrangement in which the follow-up link DO acts on the flapper valve through a lost through such a connection. In Fig. 12 the follow- .up link D is connected to a lever 0C which is pivoted at O to the free end of a lever LC. The latter is journalled on the flapper valve supporting shalt d and the lever LC carries a pin 0," between the shaft d and pivot O and adjacent the latter which is in frictional engagement with an elongated spring 0 secured to the head D of the unit D, and shaped to engage the pin OP in all positions of the latter. The lever 0C is permitted a limited turning movement relative to the lever LC about their pivotal connection 0 by virtue of the fact that the lever 00 has fingers or jaws O separated by a distance substantially greater than the diameter of a pin 0 secured to the lever LC and extending between the jaws O. A bell crank lever MC which may be identical with the previously described lever MA, is journalled on a pivot pin 0 carried by the layer LC, and has one arm connected to the actuating lever K, the other arm of lever MC carrying a pin M engaging a portion of the flapper valve dc, so as to give the latter opening movements and restrict its closing movements under the bias closing force which may be. applied to the flapper valve as in the construction shown in Figs. 1-6.

"Except when prevented by engagement of the pin 0 with one or the other of the jaws 0, the lever 0C tends to oscillate about the point of contact with the friction spring 0 of the pin 0",

- in response to any force acting on the lever 00 and tending to change its position.

When the lever MC is turned counter-clockwise, as seen in Fig. 12, to give an opening adjustment to the valve do, the resultant downward follow-up movement of the link D0 will cause the lever 00 to turn counter-clockwise, because of the frictional engagement of pin 0 and spring 0 unless and until the upper jaw O is in engagement-with the pin 0. The

.vave do is thereby given a further opening or initial eflect movement until the engagement of pin 0 with the upper jaw 0 occurs. With the upper jaw 0 in engagement with the pin O downward movement of the link D0 will cause the levers OC and LC to turn clockwise in unison about the shaft d, and through the lever LC will move the lever MC to permit a closing or-follow-up movement of the flapper valve dc. As in Figs. 10 and 11, a reverse movement of the link DO, as leakage into restriction D occurs,

and while the lever MC is stationary or while movement of lever MC in the original direction is less than the effective movement of link D0, will. result in pin 0 traversing the jaw space until the latter is brought into contact with lower jaw O concurrently moving lever. OC counterclockwise ab t pivot Ci to close valve do and thus remove e initial effect. Converse actions occur when the-lever K adjusts the lever MC in 'the clockwise direction, as seen in Fig." 12.

I Thus in operation the device of Fig. 12 is like the device of Figs; 10 and 11. With the apparatus of Figs. 10 and 11, 12 the elements DO and 0B. ocprespectively, are returned to predetermined normal positions when the pressures acting on the inner and outer sides of the bellows D are equal and that bellows has assumed its normal length. If the nozzle characteristics are symmetrical, .the device will tend to maintain average and balanced movementsof the parts whereby pins 0L, 0 will be returned to the center of slots N and O.- The embodiment of to normal provisions are made in a mechanism generally of the type shown in Figs. -12.

The form of the invention shown in Figs. 13, 14, and .15, comprises a lost motion connection between the follow-up link DO and the flapper valve dd, and also comprises return to normal provisions, analogous in their general operative effect to the provisions including the lever P of the construction shown in Figs. 7-9. In Figs. 13, 14, and 15, the follow-up link D0 is connected to a portion OD of a lever OD pivotally supported on the shaft d on which the flapper valve dd is mounted. The lever MD to which the lever K is connected, carries a pin M acting. on the flapper valve dd, and is pivoted on a pivot pin L carried by a lever LD which is journalled on the shaft d. A lost motion connection between the levers OD and LD comprises a disc ND, like the previously described disc NA, which is angularly adjustable on a supporting pin 0 carried by a portion OD of the lever OD. The tapered slot N of the disc ND receives a pin L carried by the lever LD.

The action of the lever CD on the lever LD through the disc ND and pin L, is modified by a second connection between those levers, comprising a lever member 0L pivotally connected to the lever OD through a pivot pin 0 and formed with an elongated slot OI. receiving the pin L A spring member OL" secured to the .lever OL bears resiliently against the side of a post D supported by, and projecting .away from the head D of the unit D. Angular move ment about the shaft d in either direction, given the member CD by the link DO, and occurring while the pin L is out of engagement with either curved slot wall of the disc ND, operates through the lever 0L to move the lever LD about the shaft d in the opposite direction. The lever LD is then so moved by the lever. 0L as the result of the turning movement of the latter about the point of frictional contact of its spring 0L with the post 13. The effect of the movement thus imparted to the lever OL through the lever 0L is to increase the initial opening or closing adjustment of the flapper valve DD, and thus increase the initial kick, not merely by retarding the resultant follow-up adjustment in the opposite direction of the flapper valve, but by actually giving a further adjustment in the same direction as the initial adjustment;

After the turning movement of the lever OL. has brought the, pin L into engagement with one or the other of the curved walls of the slot N, further movement of the lever OD produces a corresponding movement of the lever LD about the shaft d and thereby efiects a follow-up adjustment of the flapper valve in a direction opposite to, and partially neutralizing the initial adjustment of that valve.

The return to normal provisions included in the mechanism 'of Figs. 13, 1t, and 15, comprise a member PD movable in a direction generally radial to the shaft d. As shown, the member PD is formed at one end with an open endedconnected to the head D of the unit D by a pin and slot connection comprising a pin P carried by the part PD and working in a slot 10 extending in the general direction of the length or the member PD, and formed in a bracket member D" secured to the head D. At the opposite side of the shaft d from the pin P, the

- member PD is provided with lateral extensions P and P at the opposite sides of the plane passing centrally through the slot P and pin In the normal position oi the parts, the projections P" and P" bear against straight edge portions 0 and L of the levers OD and LD, respectively. A spring P acting between the head D and the member PD, constantly urges the latter toward the position in which both of its projections P" and P engage portions of ---parallel to shaft d and carried by the bracket D".

Element Pd carries a pin P." working in a slot 0 formed in a portion of the lever OD extending transversely to the shaft d. A tension spring P", is connected at one end to an arm portion of the member Pd and at its opposite end-to a threaded adjusting part P" adjustably connected to a bracket D carried by the housing or body of the unit D. The spring P tends to hold the member Pd in the position in which said spring is radial to the pivot D", and in which the pin P" through its engagement with the sides of the slot 0", holds the lever OD in its normal position. The analogy of slot N and spring P" will be more clearly seen when it is considered that if in Fig. 3 the lever L and 0 were .made integral and slot N omitted and an adjustable spring such as spring P" were applied to pivot M radially to'pivot d when the'parts were in normal position, the movements of link DO from normal position would be variably opposed in accordance wth the existing tension in the spring with the same eflect that slot N variably changes the lever ratios in accordance with its existing angular position, whenever DO moves Irom its normal position. In the device 0! Figs. 31-15 the member OD which is directly actuated by link DO, corresponds to the member 0 of Fig. 3 and when in its normal position the lever 0D.is given no turning movement by spring P" because the line of action of the spring is then radial. to the axis of shaft D Deflection oi member 0D trom its normal position under the action of link D0 will be retarded, however, by an amount depending upon the adjustment of spring P", so that releasing the tension of the latter by the adjusting means I)" will permit a greater turning movement of lever OD in response to a given force on link DO.

In operation, on a change in the control condition resulting in an adjustment of the damper valve dd through the levers K and MD, the resultant follow up movement of the link DO-turns the leverOD in the corresponding direction about the shaft d. The initial portion of that move- -ment of the lever OD about the shait d' in one gagement oi' its spring 0L". with the post D.

Such initial turning movement of the lever LD augments the initial kick efl'ect,-by a further adjustment of the valve dd in the directionoi its original adjustment eil'ected through the levers K and MD. The initial turning movement of .the lever LD terminates on the engagement of the pin LF carried by the lever LB with one or the other of the curved walls of the slot N in the lost motion disc ND carried by the lever OD. Thereafter a continuation of the follow up tuming movement oi the lever OD reverses the direction of rotation of the lever and causes the latter to turn about the shaft d' 01' the lever ID in the same direction as the lever OD to thereby partially neutralize the initial adjustment of the flapper valve dd eilected by e levers K and MD.- When the follow up movem' of the link D0 is completed, and the link moves in the opposite direction as a result of the compensating action of the bellows 'D', the resultant initial return movement oi! the lever. OD causes the lever .01! to again pivot on the post D until the relative movement of the pin I and disc MD carries the pin LD across the slot N. This correspondingly delays. the initiation of the compensating adjustment of the valve dd, which does not begin until the lever LD starts to move in the same direction as the lever OD, as a result of the engagement 0! the pin U with the opposite wail of the slot N. from that engaged during the follow up adjustment of the lever LD.

Whenever conditions are stabilized long enough for the purpose. the return to normal provisions return the levers 0L and CD to their predetermined normal positions. When so returned, the pin L will be tn'its mid position betweenthe opposite curved walls of the slot N, and, through its connection with the lever 0L, will hold the latter in a corresponding intermediate normal position, so that some delay is insured in the follow up adjustment produced after, and as a result oi, the next adjustment of the flapper valve dd through the levers K and MD. As will be apparent, the extent 01' that delay will be a function oi the extent of adjustment given the flapper valveand lever ID by the levers K and MD, since the greater the initial adjustment of the flapper valve and lever OL, the greater will be the movement of the lever OD required to produce the relative movement of the pin L across the slot M and into follow-up engagement with a curved wall 0! the latter.

The embodiment of the invention illustrated in Figs, 16 and 17, comprises a mechanism which in its general organization, is generally like that of Figs. i-8, but diners from the latter in the character oi the through which the movements of the, lever LE, corresponding to the lever L of Figs. 1-6, are guided and controlled to modify the follow up adjustment, and diilers, also, in that it includes return to normal provisions.

The mechanism of Figs. 16 and 17 includes parts de, d, OE, 0', LE, ME, M, M, and LP, corresponding respectively, to the parts d, d, O, O, L, M, M311, and L of Figs. 1-8. The single member N oi Figs. 1-6, however, is replaced in Figs. 16 and 1'1, bytwo overlapping cut away or recessed discs NE and 11,-mounted side by side for independent angular adjustment in the supports N and N, and collectively turning a slot or space, which receives the pin IF carried by the lever LI but diflers in shape from the slot N in the member N. The width oi the slot or space receivim the pin L increases with the distances from the axes otthediscsNlandn. litoneside'oithat axis, one wall oi the slot or space is formed by the straight edge portion N o! the cut awaydisc 

